Let us make some entirely plausible assumptions about the outcome of the general election. Let us assume that the Conservatives attract the largest share of votes, but fall short of a majority either of votes or of seats. Let us assume that Labour comes second or third in terms of the number of votes but might actually win the greatest number of seats, though still well short of a parliamentary majority. And finally let us assume that the Liberal Democrats score well – and perhaps substantially better than was expected at the outset of the campaign – in both votes and seats and, as a necessary consequence, hold the balance of power.

The first issue will be for the Queen and her advisers. In such circumstances, who does Her Majesty ask to form a government? Do her advisers stick to precedent and advise that Gordon Brown, as the incumbent and commanding the greatest number of seats, should get the nod? Or do they pay attention to the pre-election assertion by Nick Clegg that, as a proponent of proportional representation, he would support only the Party leader who had gained the biggest share of the vote?

I suspect that the advisers would initially stick to precedent and that Gordon Brown would be asked to give it a try. I further suspect that, unless he were prepared to give a guarantee of a referendum on electoral reform, his attempt would founder on Clegg’s determination to stick to his guns. The failed attempt could, however, take some time before the failure became definitive.

The Queen would then ask David Cameron to form a government. He would seem to have a better chance of success, being able to argue that he had won the greatest share of votes. Nick Clegg would again try to extract a major commitment on electoral reform, but Cameron would refuse to accommodate him. Clegg would, however, be compelled, for fear of being accused of irresponsibility and of forcing a second and unwanted election on the country, to do some sort of deal to allow Cameron to form a government.

That deal would probably fall short of a formal coalition but might take the form of an undertaking to support the new government on issues of confidence and supply. It might be time-limited, but whether or not the deal included any such formal provision, the issues of how long it might last and of the circumstances in which it might be brought to an end would constitute the real story of the 2010 general election.

The parties to the deal, both Cameron and Clegg, would have clear but conflicting strategic objectives. Both could imagine scenarios which would greatly advance their parties’ interests.

Cameron would hope to emulate the experience of other leaders of minority governments who had used the prestige of government to underpin their electoral appeal and to push on in a second election to achieve an overall majority. Harold Wilson pulled this trick off twice.

But it might not be so easy this time. Cameron has to grapple with urgent and desperate issues. He either begins to deal with them effectively and accepts the pain that will inevitably attend such an enterprise, or he ducks the issues and is easily attacked as failing to attack the country’s all too obvious problems. A year or two into a new Tory government, and the voters could be – one way or another – badly disappointed. The honeymoon this time might be a very short one.

For Nick Clegg, the issues are almost equally daunting. His task will be to pull the plug on the new government at a time when he won’t be accused of irresponsibility and of plunging the country into further electoral turmoil. He will want an issue which will, from both a position of principle and of prospective electoral advantage, allow him to go to the country as the alternative government. He will argue that while he had played his part in providing stable government he could no longer support a Tory-led administration that was heading down the wrong path. But his long-term objective would rest on the assertion that the Lib Dems were now the only party that could both defeat the Tories and form a stable majority government.

It is now 100 years since Labour began its push to supplant the Liberals as the alternative to the Tories. The Conservatives, like the poor, are always with us (and some would argue that there is a causal connection between the two propositions). The perennial question in British politics is as to who will constitute the alternative. Today’s Liberals have their sights on the real possibility of reversing 100 years of history.